In recent years, with respect to an electronic device, etc., demands for space saving of the installation place and weight reduction are increasing. In addition, along with an increase in the localization of a control mechanism or the cloud utilization, the demand for smaller size and higher performance of an electronic device is growing. Consequently, the quantity of heat generated from the device is increased, and it is required to develop a thermal conductive element more excellent in the thermal conductivity. For example, a thermal conductive element is used in the technical field of a semiconductor device employed for, e.g., a high-brightness LED, a personal computer, an automotive motor control mechanism, or a device utilizing power electronic technology of converting and controlling electric power.
The thermal conductive element is used around an electronic component and therefore, is required to have high insulating property in addition to high thermal conductivity.
From such a viewpoint, a thermal conductive sheet containing a resin and an aluminum nitride powder is used as a thermal conductive element exhibiting high thermal conductivity and high insulating property.
However, the conventional thermal conductive sheet has a problem that when it is used in a wet environment, aluminum nitride reacts with water to generate aluminum hydroxide, whereby the thermal conductivity is reduced, or a problem that ammonium ion is also produced by the above-described reaction and ion migration is caused by the ammonium ion, as a result, the insulating property is reduced.
From such a viewpoint, there have been proposed, for example, an aluminum nitride powder subjected to a surface treatment with an inorganic phosphoric acid compound (Patent Document 1), an aluminum nitride powder subjected to a surface treatment with an organic phosphoric acid compound and then subjected to a heat treatment at a temperature of approximately from 150 to 800° C. (Patent Document 2), and an aluminum nitride powder subjected to a surface treatment with an organic silicon compound at a high temperature (Patent Document 3).